1. Field of the Invention
The present invention relates to an optical coupling apparatus for detecting a matter to be detected, and to a method for manufacturing said optical coupling apparatus.
2. Description of the Related Art
With reference to FIGS. 12 to 15, a process for manufacturing a conventional optical coupling apparatus will be described hereinbelow. Firstly, as shown in FIG. 12, on a substrate 101 are formed wiring patterns 102a to 102d. The substrate 101 is provided with holes 101a, and a plating layer 103 is so formed as to cover an inner wall of each of the holes 101a and the periphery thereof. Then, on each of the wiring patterns 102a is mounted a light-receiving element 104, and on each of the wiring patterns 102c is mounted a light-emitting element 105. The light-receiving elements 104 are each connected to their respective wiring patterns 102b via a bonding wire 106, and the light-emitting elements 105 are each connected to their respective wiring patterns 102d via a bonding wire 107.
Subsequently, as shown in FIG. 13, by a transfer molding operation, primary molded bodies 111 and 112 are formed from light-transmitting resin so as to cover the light-receiving elements 104 and the light-emitting elements 105, respectively. That is, the light-receiving and light-emitting elements 104 and 105 are contained in the primary molded bodies 111 and 112.
Further, as shown in FIG. 14, by an injection molding operation, a secondary molded body 113 is formed from light-shielding resin, in such a way as to fill in the gap between the primary molded bodies 111 and 112, and to fill in a recess 112a of the light-emitting-element 105-side primary molded body 112. This configuration helps keep the light-receiving element 104 from incidence of light that has been emitted from the side face of the light-emitting element 105 and then reflected from components arranged around the coupling apparatus. Moreover, since the secondary molded body 113 cannot be bonded to the primary molded body 111, 112 because of their difference in material, light-shielding resin is poured into each of the holes 101a of the substrate 101 and is then solidified, so that the secondary molded body 113 is fixed to the substrate 101.
Thereafter, the construction is subjected to dicing along broken lines shown in FIG. 14 to obtain two pieces of optical coupling apparatuses 121 as shown in FIG. 15.
As shown in FIGS. 16 to 18, in reality, a larger number of continuously-arranged optical coupling apparatuses are fabricated concurrently, and they are separated from one another by dicing. For example, on a substrate measuring 46 mm by 136 mm is formed a 16 by 38 array of optical coupling apparatuses (608 pieces in total), and the construction is subjected to dicing to separate the optical coupling apparatuses from one another.
In the optical coupling apparatus 121, detection of a to-be-detected matter is carried out as follows. The light-emitting element 105 is driven to emit light, and the light reflected from the to-be-detected matter is guided in such a way as to be incident on the light-receiving element 104. Alternatively, there is formed an optical path for guiding light from the light-emitting element 105 toward the light-receiving element 104. In the latter case, the to-be-detected matter is detected on the basis of variation in the output of the light-receiving element 104 as observed when the optical path is blocked by the to-be-detected matter.
Incidentally, the primary molded bodies 111 and 112 are formed as follows. As shown in FIG. 19, an upper mold 131 and a lower mold 132 are placed so as to have sandwiched therebetween the substrate 101. After the upper and lower molds 131 and 132 are closed, light-transmitting resin is filled in cavities 133 and 134 of the upper mold 131. At this time, as shown in FIG. 20, a protrusion 131a of the upper mold 131 is brought into press-contact with the periphery of the hole 101a of the substrate 101 to cover the hole 101a. This prevents the light-transmitting resin from entering the hole 101a. Although, in this figure, the substrate 101 is taken as a minimum unit that corresponds to a single optical coupling apparatus, in reality, as shown in FIGS. 16 to 18, a large-sized substrate corresponding to a multiplicity of continuously-arranged optical coupling apparatuses is sandwiched between the upper and lower molds.
However, such a conventional construction encounters the following problem. In general, the components constituting the optical coupling apparatus, such as the substrate 101, the plating layer, and the resist layer are each given certain thickness tolerance, and thus a layered body composed of the components including the substrate 101 incurs an uneven thickness. That is, the layered body varies in thickness from part to part, giving rise to lack of uniformity in the thickness. Hence, the region of the substrate 101 around a multiplicity of the holes 101a also incurs uneven thickness. Meanwhile, the dimensions of the upper and lower molds 131 and 132 are determined on the assumption that the layered body has a uniform thickness. Thus, in a case where the region of the substrate 101 around the holes 101a is made smaller in thickness than the gap between the protrusion 131a of the upper mold 131 and the lower mold 132, it is impossible to bring the protrusion 131a of the upper mold 131 fully into press-contact with the periphery of the holes 101a, which results in a gap having a size of a few tens of μm being developed between the protrusion 131a of the upper mold 131 and the periphery of the holes 101a. As a result, part of the light-transmitting resin finds its way into the holes 101a through the gap, and thereby the holes 101a are blocked up.
If the holes 101a of the substrate 101 are filled with the light-transmitting resin in that way, the light-shielding resin is prevented from entering the holes 101a of the substrate 101. This causes the secondary molded body 113 to come off from the substrate 101. To prevent this, upon completion of the molding of the primary molded bodies 111 and 112, whether the light-transmitting resin has gotten into the holes 101a or not is checked. If the intrusion is confirmed, the light-transmitting resin trapped in the holes 101a is manually removed. In order to facilitate the removal of the light-transmissive resin, as described previously, the plating layer 103 is formed so as to cover the inner wall of the hole 101a and the periphery thereof.
Moreover, the dimension of the lower mold 132 is so determined that the layered body composed of the substrate 101, etc. protrudes slightly beyond the lower mold 132. This causes, when the upper and lower molds 131 and 132 are put together, the upper mold 131 to be brought fully into press-contact with the slightly-protruding layered body.
In this case, however, the uneven thickness of the substrate 101 in particular becomes problematic. In the manufacturing process, since a multiplicity of substrates are dealt with, the uneven thicknesses of these substrates lead to variation in the length of the jutted part of the layered body from the lower mold 132. Consequently, the upper mold 131 fails to fully make press-contact with the layered body, or the pressure exerted on the layered body becomes unduly great, which results in breakage of the layered body.
In view of the foregoing, as shown in FIG. 21A, there are prepared a plurality of shims 141 having mutually different thicknesses. Then, as shown in FIGS. 21B and 21C, the one having a suitable thickness selected from among the shims is arranged between the substrate 101 and the lower mold 132, so that the layered body composed of the substrate 101, etc. protrudes beyond the lower mold 132 appropriately.
Practically, a multiplicity of substrates are classified according to the thickness before delivery. Thus, selection of the shim is made according to the thickness of the substrate. However, prior to setting the shim in the lower mold 132, the shim needs to be selected on a substrate-by-substrate basis, which leads to remarkably poor operation efficiency. Furthermore, it is necessary to make a request of substrate manufacturers for measurement of the thickness of the substrate and submission of the measurement data. This increases the cost required for the production of the substrate.
Meanwhile, the substrate has a plurality of holes formed thereon for positioning the substrate relative to the mold. With respect to the positions of these holes, the primary and secondary molded bodies are formed separately using different molds.
However, an adverse effect is likely to occur because of synergy between a molding error as observed in the primary molded body and that observed in the secondary molded body, which may result in defective pieces of optical coupling apparatuses being produced. In this case, prior to forming the secondary molded body, by properly adjusting the positioning of the substrate relative to the mold at the discretion of workers concerned, the mutual errors between the primary and secondary molded bodies can be minimized. However, to achieve this, the workers are required to have a great deal of skill, and the operation efficiency is impaired.